The invention concerns a locking cover for a piping connection, in particular, for an automobile gas tank cap. It comprises a sealing flange which engages the piping connection as well as a radially located sealing flange, on the inner-part of the cap. An outer cap made of flexible material engages the sealing flange and is held to it via a locking mechanism. The locking mechanism has radially directed projections from the inner side of the wall of the cap. These projections on the inside of the cover and outer cap engage the sealing flange from behind and at the same time engage a guide surface directed toward the base of the cap in such a way as to provide a firm connection adjacent to the sealing flange.